Pancreatitis is the most frequent complication of endoscopic retrograde cholangiopancreatography (ERCP), accounting for substantial morbidity, occasional mortality, and increased health care expenditures. Until recently, the only effective method of preventing post-ERCP pancreatitis (PEP) had been prophylactic pancreatic stent placement (PSP), an intervention that is costly, time consuming, technically challenging, and potentially dangerous. We recently reported the results of a large randomized controlled trial demonstrating that rectal indomethacin, a non-steroidal anti-inflammatory drug, reduced the risk of pancreatitis after ERCP in high-risk patients, most of whom (>80%) had received a pancreatic stent. Secondary analysis of this RCT suggested that subjects who received indomethacin alone were less likely to develop PEP than those who received a pancreatic stent alone or the combination of indomethacin and stent, even after adjusting for underlying differences in subject risk. If indomethacin were to obviate the need for PSP, major clinical and cost benefits in ERCP practice could be realized. Objective: To assess whether rectal indomethacin alone is non-inferior to the combination of rectal indomethacin and prophylactic pancreatic stent placement for preventing post-ERCP pancreatitis in high-risk cases. Methods: We are proposing a comparative effectiveness multi-center non-inferiority study of rectal indomethacin alone vs. the combination of rectal indomethacin and prophylactic pancreatic stent placement for the prevention of post-ERCP pancreatitis in high-risk patients. One thousand four hundred and thirty subjects at elevated risk for PEP who would normally receive a pancreatic stent for prophylaxis will be randomized to indomethacin alone or the combination of indomethacin and PSP. The proportion of patients developing PEP and moderate-severe PEP will be compared. In addition, we will establish a quality-assured central repository of biological specimens obtained from study participants, permitting future translational research elucidating the molecular and genetic mechanisms of PEP, as well as the mechanisms by which non-steroidal anti-inflammatory drugs prevent this complication.